Polydextrose is a water-soluble, low calorie non-cariogenic bulking agent. It is a randomly cross-linked glucan polymer produced through the acid-catalyzed condensation of glucose. Rennhard U.S. Pat. No. 3,766,165 and Rennhard U.S. Pat. No. 3,876,794 detail the preparation of polymeric glucose and maltose products by anhydrous melt polymerization using non-volatile, edible, organic polycarboxylic acids as catalysts, cross-linking agents or polymerization activators.
Polydextrose is an essentially non-nutritive carbohydrate (approximately 1 calorie/gram) substitute. It provides a substitute for sugar and has many of the desired technological properties of sugar, but does not have the sweetness. This non-sweet bulking capability is advantageous where conventional sugar-based compositions have proven to be too sweet. Moreover, this non-sweet bulking capability is especially advantageous when used in combination with high intensity sweeteners to provide low-calorie food products having the desirable texture of conventional sugar-containing food products without the calories associated with the sugar.
Polydextrose is commercially available in three forms, Polydextrose A, an amorphous, slightly acid fusible powder, Polydextrose N, a neutralized, light-colored 70% solution of Polydextrose A, and Polydextrose K, a neutralized powder form of Polydextrose A. As the polymerization process produces a mixture of polysaccharides and saccharide residuals, none of these products is a pure polydextrose product. All of these polydextrose products include a variety of low molecular weight compounds, such as glucose, sorbitol, citric acid and oligomers, which contribute to the calorie value of these products. In addition, all of the polydextrose products also include other low molecular weight compounds such as 1,6-anhydroglucose (levoglucosan) and 5-hydroxymethylfurfural which give these products a bitter taste and musty off-flavor. Although these low molecular weight compounds are found in polydextrose products only in small amounts (1,6-anhydroglucose, about 4%, bitter taste) (5-hydroxymethylfurfural, about 0.1%, musty off-flavor), those amounts are significant enough to negatively impact on the usefulness of polydextrose in most food products when polydextrose is present in medium to high levels.
Torres U.S. Pat. No. 4,622,233 discloses a first method of treating polydextrose by decolorizing with a bleaching agent and thereafter purifying the decolorized material. A further method disclosed and claimed in the Torres '233 disclosure for reducing color, glucose content and anhydroglucose content of Type A polydextrose includes the following steps: (a) contacting a 60-70% (W/W) aqueous solution of polydextrose Type A with a food-approved bleaching agent at a temperature of 25.degree. -90.degree. C. and a pH of about 2.5 to about 9.0; (b) adjusting the pH of the product of step (a), if about 7, to about 6; (c) adding one or more of the solvents selected from the group consisting of methanol, ethanol and ethylacetate such that said solvent includes 50-80% (W/W) of the mixture; and (d) filtering the final product, and, if desired, drying. The Torres '233 patent ties decoloration to purification which is not n Moreover, decoloration can be an undesired process requirement and condition which produces its own additional problems. For example, when the polydextrose purified by the Torres '233 method is subjected to high heating, such as in cooking, the coloring returns to the substance. In addition, the bleaching step leaves residuals which are difficult to remove. Furthermore, extra steps are required by Torres which require additional time, handing, and energy.
U.S. patent application Ser. No. 043,793, filed Apr. 29, 1987, entitled "Method of Purifying Polydextrose and Composition Containing Same" and assigned to Warner-Lambert Company, assignee of the present application, discloses a process for providing a purified, unbleached polydextrose product wherein an aqueous solution of polydextrose in a concentration of from about 10% to about 90% is intimately contacted with a polar organic solvent such as ethanol or acetone. The ratio of polydextrose to solvent is from about 5% to about 4% by weight of polydextrose to about 35% to about 85% by weight of solvent. The mixture is then allowed to equilibrate to form a substantially contaminantcontaining fraction and a substantially polydextrosecontaining fraction. The fractions are then separated for use of the polydextrose-containing fraction.
Generally, osmosis refers to a process whereby a pure liquid (usually water) passes through a semipermeable membrane into a solution (usually sugar or salt and water) to dilute the solution and achieve osmotic equilibrium between the two liquids. In contrast, reverse osmosis is a pressure driven membrane process wherein the application of external pressure to the membrane system results in a reverse flux with the water molecules passing from a saline or sugar solution compartment into the pure water compartment of the membrane system. Reverse osmosis membranes also allow a variety of aqueous solutes to pass through them while retaining selected molecules. It is a method of removing dissolved components of a material without a phase change. This is advantageous in that reverse osmosis purification presents a substantial energy savings over conventional steam distillation or other vaporization techniques. It is especially advantageous where heat labile and/or volatile desirable components to be retained are present.
Reverse osmosis membranes are very thin semipermeable membranes characterized in their composition, molecular weight cut-off (MWCO), and rejection properties, that is, their total capacity to retain specific molecules while allowing the solute and other, generally smaller or opposite charged molecules, to pass through. The idea in selecting a reverse osmosis membrane is to optimize the permeability, MWCO, and rejection characteristics for a particular application.
Reverse osmosis has been used for water purification including salt removal for potable water or water for injection. It is now being applied to concentration and purification of low molecular weight pharmaceutical products, such as antibiotics, peptides and amino acids.
Adams et al., U.S. Pat. No. 3,544,455 discloses a process for purifying aqueous solutions of itaconic acid of inorganic salts, colored matter and organic impurities by use of reverse osmosis. Pressure is applied to the solution and a semipermeable membrane which allows passage of the itaconic acid and water, but not the impurities, is utilized. Stana et al. U.S. Pat. No. 4,206,049. discloses a method for concentrating and recovering uranium from a phosphoric acid solution using a reverse osmosis membrane system, a means for iron precipitation and removal, and subsequent evaporation and ignition of organic impurities. Kaneko et al. U.S. Pat. No. 4,601,829 discloses a process for purifying lysine including separating lysine from aqueous ammonia by use of a cation exchange resin, a reverse osmosis membrane system and a means for. concentrating the liquids such that removal of ammonia is achieved.
It has now been found that polydextrose can be purified by reverse osmosis techniques to remove greater amounts of 1,6-anhydroglucose, 5--hydroxymethylfurfural and other low molecular weight manufacturing contaminants to provide an organoleptically improved polydextrose. The reverse osmosis technique allows for removal of greater amounts of impurities in a short processing time without use of organic solvents. A high yield is achieved at a low cost. This new product, polydextrose purified by reverse osmosis, containing greatly reduced amounts of manufacturing contaminants such as 1,6anydroglucose and 5-hydroxymethylfurfural, can be utilized in products for oral ingestion such as food products in much greater concentrations, even as high as about 99%, without any bitter taste or musty off-flavor and without the need to use masking agents to disguise the unpleasant taste qualities. Accordingly, this new improved polydextrose would have great utility as a low calorie non-sweet bulking agent in many products for oral ingestion including food products, and especially confections.